Our earlier application Ser. No. 678,832, filed Apr. 21, 1976, describes a group of 3-mercapto-7H-pyrazolo- [4,3-e]-1,2,4-triazolo[4,3-c]pyrimidines unsubstituted or lower alkyl substituted in the 7- and/or 9-positions as well as derivatives in which the sulfur in the 3-position bears various substituents. These previously described compounds are obtained, according to one method, from a 1-and/or 3- unsubstituted or substituted 4-halopyrazolo[3,4-d]pyrimidine by sequential treatment with hydraxine and 1,1-thiocarbonyl diimidazole.
It has now been found that treatment of the same unsubstituted or substituted 4-halopyrazolo[3,4-d]pyrimidine with a monosubstituted hydrazine instead of hydrazine and then with 1,1-thiocarbonyldiimidazole yields a 1,7-dihydro-1- substituted -3H-pyrazolo[4,3-e]-1,2,4-triazolo[4,3-c]pyrimidine- 3-thinoe meso-ionic didehydro derivative, an inner salt or meso-ionic form in which the sulfer has a negative charge and a nitrogen has a positive charge, and the substituent on the original hydrazine reactant is now in the 1 -position. The same meso-ionic derivatives can also be obtained by utilizing carbon disulfide instead of 1,1 -thiocarbonyldiimidazole. Similarly, when 1,1-carbonyldiimidazole is used instead of 1,1- thiocarbonyldiimidazole, the analogous oxygen containing products are obtained.